Mephedrone, systematic name (RS)-2-methylamino-1-(4-methylphenyl)propan-1-one, is a designer drug of the cathinone class of stimulants, implicated in a number of drug-related fatalities. It is illegal in a number of countries world-wide. Although illegal in many countries, recent studies highlighted that the accessibility and popularity of the drug is undiminished due to a re-branding approach by suppliers in which ‘alternative’ mephedrone products under the name of NRG-1 (Energy 1), and stated as being legal highs containing naphthylpyrovalerone, in fact contain mephedrone (Brandt et al. 2010a; Brandt et al. 2010b). The metabolism of mephedrone occurs via various combinations of oxidation of the methyl group attached to the benzene ring, N-demethylation and reduction of the keto functionality (Meyer et al. 2010). There is great potential for adverse events or abuse in individuals taking or with access to mephedrone, especially in its form as NRG-1 which by marketing as a legal high gives the impression of safety. Therefore, there is a need in clinical and forensic toxicology for its detection and/or determination using practical and inexpensive analytical methods. Analytical methods that have been used to detect and determine mephedrone and its metabolites include gas chromatography linked to mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) (Brandt et al. 2010a; Wood et al 2010; Meyer et al. 2010). A less costly and practical immunoassay has, to the inventors' knowledge never been reported for the detection or quantification of mephedrone or its metabolites.